This invention relates generally to dynamoelectric machines and, more particularly, to fluid lubricant (oil) wicking arrangements for maintaining lubricant at the bearing surface.
In small motors, such as fractional horsepower motors, the practice has been to use sleeve bearings in a housing filled with wicking material for retaining an appreciable quantity of oil and supplying it as needed to the bearing surface. The wicking material may be any of a variety of shredded or particleized materials compacted together to a suitable density for oil retention. Wool felt has been a widely used material as have cellulosic materials such as those made of wood fibers or cotton linters as disclosed in U.S. Pat. Nos. 2,966,459 and 3,466,244 respectively. A frequently used arrangement is one in which the bulk of the wicking material comprises cellulosic fibers as in the referred to patents in combination with a feeder wick, such as of wool felt, that extends from the bearing housing in intimate contact with the cellulosic wicking material through a window in the bearing sleeve for supplying oil to the bearing surface. Such an arrangement is shown, for example, in U.S. Pat. No. 3,184,272.
Another type of wicking material that has been proposed is exemplified by U.S. Pat. No. 3,190,842, issued June 22, 1965 which relates to open cell foamed plastic material such as polyurethanes. While feasibility of such materials as oil wicks is believed to exist, experience by the present inventor with open cell plastic material tends to indicate that readily available materials are not of sufficient density or do not have sufficiently small cell openings for adequate oil retention and therefore have not superseded materials such as the cellulosic particulate wicking materials referred to above.
Self-lubricated bearings are those in which provision is made to return oil from the shaft to the wicking material so as to require no lubrication or very infrequent lubrication during normal operation. This is accomplished by having one or more radially projecting elements mounted on the shaft that both tend to prevent axial flow of the lubricant away from bearings and also as oil builds up, fling it radially outward where it is collected by an exposed surface of the wicking material. It is found that such lubrication arrangements can sometimes prove defective because wicking material from the exposed surface becomes loose and strings of it extend from their intended location down to the shaft. As a result, oil can run along the shaft away from the oil flinger and the bearing. While most likely to occur in vertically mounted motors, this problem can also occur in horizontally mounted motors.